The interior constitution of a connecting rod type of hermetic compressor according to the prior art is shown in FIG. 1. Referring to this figure, an airtight container 1 composed of an upper container 1t and a lower container 1b is provided, and a frame 2 is installed within the airtight container 1. A stator 3 is fixed to the frame 2 which is in turn supported in the airtight container 1 by a spring 2S.
Further, a crankshaft 5 is installed through a central portion of the frame 2. The crankshaft 5 is integrally provided with a rotor 4, and thus, is rotated together with the rotor 4 by means of electromagnetic interaction with the stator 3.
At an upper end of the crankshaft 5, an eccentric pin 5b is formed to be offset from a center of rotation of the crankshaft 5. In addition, a counterweight 5c is formed at a side opposite to the eccentric pin 5b. At a lower end of the crankshaft 5, a propeller 5d for sucking up oil L residing at the bottom of the lower container 1b into an oil passage 5a formed through the crankshaft 5 is installed.
Furthermore, a cylinder 6 with a compression chamber 6′ formed therein is integrally formed in the frame 2. Further, a piston 7, which is connected to the eccentric pin 5b of the crankshaft 5 through a connecting rod 8, is installed in the compression chamber 6′.
Here, as shown in FIG. 2, the eccentric pin 5b is connected to a crankshaft connecting portion 8a of the connecting rod 8, and the piston 7 is connected to a piston connecting portion 8b of the connecting rod 8 through a piston pin 7′. A sleeve SL is press-fitted between the crankshaft connecting portion 8a and the eccentric pin 5b. At this time, an external surface of the sleeve SL is pressed by an inner surface of the crankshaft connecting portion 8a so that the sleeve SL is rotated integrally with the connecting rod 8. The piston pin 7′ is connected to the piston connection portion 8b in a state where it is press-fitted into the piston 7.
In addition, a valve assembly 9 for regulating a refrigerant introduced into and/or discharged from the compression chamber 6′ is installed at a leading end of the cylinder 6. The reference numeral 10 denotes a head cover, the reference numeral 11 denotes a suction muffler, the reference numeral 12 denotes a suction pipe for transferring the refrigerant into the airtight container 1, and the reference numeral 13 denotes a discharge pipe for discharging the refrigerant to the outside of the compressor.
In the compressor constructed as such, when electric power is applied to the compressor, the rotor 4 is rotated by means of the electromagnetic interaction between the stator 3 and the rotor 4. Simultaneously, the crankshaft 5 is rotated integrally with the rotor 4. As the crankshaft 5 is rotated, the eccentric pin 5b offset from the crankshaft 5 revolves on an axis of the crankshaft 5. The connecting rod 8 connected to the eccentric pin 5b is interlocked with the eccentric pin 5b to cause the piston 7 to reciprocate linearly. Thus, the piston 7 causes the refrigerant to be compressed while reciprocating linearly within the compression chamber 6′.
However, there is the following problem in the prior art mentioned above.
In general, the relationship among the connecting rod 8, the piston 7 and the piston pin 7′ is as follows. The piston pin 7′ is press-fitted into the piston 7, and the connecting rod 8 and the piston pin 7′ can be slid with each other. Therefore, the piston pin 7′ is integrally fixed to the piston 7 and performs relative motion with respect to the piston connecting portion 8b of the connecting rod 8.
In order to produce the above motion, the piston pin 7′ should be press-fitted into the piston 7. However, as shown well in FIG. 3, the piston 7 is somewhat distorted in a vertical direction in this figure as the piston pin 7′ is press-fitted into the piston 7. Thus, a cross sectional shape of the piston does not become a perfect circle. It is a phenomenon that occurs because the piston pin 7′ is forcibly press-fitted into the piston 7.
If the piston 7 is distorted and its section does not take the shape of the perfect circle, the phenomenon occurs that uneven wear is produced on an inner wall surface of the compression chamber 6′ on which the piston 7 slides and the refrigerant leaks out between the inner wall surface of the compression chamber 6′ and the piston 7. Thus, compression of the refrigerant within the compression chamber 6′ cannot be properly made.